The invention relates to a blocking device for an operating piston and cylinder arrangement wherein the piston rod selectively controls the closing of the entrance to and the exit from a milking compartment after an animal has entered to be milked.
Such a cylinder and piston arrangements including blocking devices are disclosed in European application 0 548 058 of Van den Berg et al published Jun. 23, 1993.
This prior art application discloses a milking compartment with a milking robot, said milking compartment being provided with entrance and exit gates or doors. For opening the entrance door, a pneumatic operating piston and cylinder is provided. A pneumatic operating piston and cylinder is selected inasmuch as almost all the other pistons and cylinder arrangements for operating the milking robot arm are also pneumatically actuated and thus, a pneumatic operating system is available. A pneumatic operating piston and cylinder, in contrast with a comparable hydraulic operating piston and cylinder, provides less force. The above-mentioned milking compartment with a pneumatic operating piston and cylinder has the disadvantage that, when an animal leans against the entrance door, the pneumatic operating piston and cylinder is not capable of absorbing the force so exerted, unless a large pneumatic piston and cylinder is used. In the milking compartment according to European application this problem is solved in that on the entrance door a rack with a ratchet is disposed which acts as a blockage device when the animal pushes against the entrance door.
This arrangement, however, has the disadvantage of not being compact and that the operating piston cylinder and the rack with ratchet operate separately.
An object of the invention is to provide an operating piston and cylinder for the entrance and for the exit doors of a milking compartment which is compact and is relatively simple to operate.
In accordance with the invention, this is achieved by providing operating piston and cylinder with a blocking device for blocking movement of the piston rod in at least one direction, said blocking device being provided with activating means which comprises a third operating entrance into the cylinder which can be connected to conventional first or second operating cylinder entrances or to both, to place the activating means into operation. Because the blocking device is integrated in the operating piston and cylinder and the activating means are connectable to each other, the result is a compact and easily operable operating piston and cylinder that includes a blocking device.
According to an inventive feature, a fluid connection between the third operating entrance and the first or the second operating entrances or both, is effected by mechanical or electric or pneumatic or hydraulic controls. Therefore, it is possible to activate the piston and cylinder and the blocking device mechanically or electrically or pneumatically or hydraulically by means of a control signal. For the purpose of obtaining a compact construction, according to an inventive feature, the blocking device comprises a second piston provided within the cylindrical housing, which second piston is received on the same piston rod whereby the housing is divided by the two pistons into first, second, third and fourth chambers, said third and fourth chambers being provided with a fourth and fifth operating entrances, respectively. In accordance with a further inventive feature, the activating means comprise passage means connecting the third and fourth chambers that permits a fluid flow in only one direction between the third and fourth chambers. According to again another aspect of the invention, such passage means are included in the second piston or in a pipe connected to the fourth and fifth operating entrances, or in both. In a preferred embodiment of the invention, the passage means include a check or non-return valve. According to again another inventive feature, the activating means comprise a sliding valve. In a preferred embodiment of the invention, the sliding valve is activated pneumatically, but it is well within the skill of the art that the sliding valve may be activated a different manner, such as electrically or hydraulically. For the purpose of activating the sliding valve from one side, according to an inventive feature, the sliding valve comprises a return or drawback spring. In a preferred embodiment of the invention, the sliding valve is constituted by a 2/2-valve with a one-way connection and two closed gates. According to again another inventive feature, the first and second chambers may be filled with a gas, such as air, while the third and fourth chambers may be filled with a liquid, such as oil.
The invention also relates to a milking compartment which comprises a framework including an entrance door and an exit door, said entrance door or exit door or both, being provided with an operating piston and cylinder as described above. According to a further inventive feature, the milking compartment comprises a milking robot for automatically connecting teat cups to the teats of an animal to be milked.